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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the cyanobacterium Synechococcus elongatus PCC 7942, KaiA, KaiB, and KaiC are essential proteins for the generation of a circadian rhythm. KaiC is proposed as a negative regulator of the circadian expression of all genes in the genome, and its phosphorylation is regulated positively by KaiA and negatively by KaiB and shows a circadian rhythm in vivo. To study the functions of KaiC phosphorylation in the circadian clock system, we identified two autophosphorylation sites, Ser-431 and Thr-432, by using mass spectrometry (MS). We generated Synechococcus mutants in which these residues were substituted for alanine by using site-directed mutagenesis. Phosphorylation of KaiC was reduced in the single mutants and was completely abolished in the double mutant, indicating that KaiC is also phosphorylated at these sites in vivo. These mutants lost circadian rhythm, indicating that phosphorylation at each of the two sites is essential for the control of the circadian oscillation. Although the nonphosphorylatable mutant KaiC was able to form a hexamer in vitro, it failed to form a clock protein complex with KaiA, KaiB, and SasA in the Synechococcus cells. When nonphosphorylatable KaiC was overexpressed, the kaiBC promoter activity was only transiently repressed. These results suggest that KaiC phosphorylation regulates its transcriptional repression activity by controlling its binding affinity for other clock proteins.
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PMID:Role of KaiC phosphorylation in the circadian clock system of Synechococcus elongatus PCC 7942. 1536 31

P700, the primary electron donor of photosystem I, is an asymmetric dimer made of one molecule of chlorophyll a' (P(A)) and one of chlorophyll a (P(B)) that are bound to the homologous PsaA and PsaB polypeptides. While the carbonyl groups of P(A) are involved in hydrogen-bonding interactions with several surrounding amino acid side chains and a water molecule, P(B) does not engage hydrogen bonds with the protein. Notably, the residue Thr A739 is donating a strong hydrogen bond to the 9-keto C=O group of P(A) and the homologous residue Tyr B718 is free from interaction with P(B). Light-induced FTIR difference spectroscopy of the photooxidation of P700 has been combined with a site-directed mutagenesis attempt to introduce hydrogen bonds to the carbonyl groups of P(B) in Synechocystis sp. PCC 6803. The FTIR study of the Y(B718)T mutant provides evidence that the 9-keto C=O group of P(B) and P(B)(+) engages a relatively strong hydrogen-bonding interaction with the surroundings in a significant fraction (40 +/-10%) of the reaction centers. Additional mutations on the two PsaB residues homologous to those involved in the main interactions between the PsaA polypeptide and the 10a-carbomethoxy groups of P(A) affect only marginally the vibrational frequency of the 10a-ester C=O group of P(B). The FTIR data on single, double, and triple mutants at these PsaB sites indicate a plasticity of the interactions of the carbonyl groups of P(B) with the surrounding protein. However, these mutations do not perturb the hydrogen-bonding interactions assumed by the 9-keto and 10a-ester C=O groups of P(A) and P(A)(+) with the protein and have only a limited effect on the relative charge distribution between P(A)(+) and P(B)(+).
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PMID:Evidence for hydrogen bond formation to the PsaB chlorophyll of P700 in photosystem I mutants of Synechocystis sp. PCC 6803. 1580 33

The open reading frames (ORFs) encoding two potential protein-serine/threonine phosphatases from the cyanobacterium Synechocystis sp. strain PCC 6803 were cloned and their protein products expressed in Escherichia coli cells. The product of ORF sll1033, SynPPM3, is a homologue of the PPM family of protein-serine/threonine phosphatases found in all eukaryotes as well as many members of the Bacteria. Surprisingly, the recombinant protein phosphatase dephosphorylated phosphotyrosine- as well as phosphoserine-containing proteins in vitro. While kinetic analyses indicate that the enzyme was more efficient at dephosphorylating the latter, replacement of Asp608 by asparagine enhanced activity toward a phosphotyrosine-containing protein fourfold. The product of ORF sll1387, SynPPP1, is the sole homolog of the PPP family of protein phosphatases encoded by the genome of Synechocystis sp. strain PCC 6803. Like many other bacterial PPPs, the enzyme dephosphorylated phosphoserine- and phosphotyrosine-containing proteins with comparable efficiencies. However, while previously described PPPs from prokaryotic organisms required the addition of exogenous metal ion cofactors, such as Mg2+ or Mn2+, for activity, recombinantly produced SynPPP1 displayed near-maximal activity in the absence of added metals. Inductively coupled plasma mass spectrometry indicated that recombinant SynPPP1 contained significant quantities, 0.32 to 0.44 mol/mole total, of Mg and Mn. In this respect, the cyanobacterial enzyme resembled eukaryotic members of the PPP family, which are metalloproteins. mRNA encoding SynPPP1 or SynPPM3 could be detected in cells grown under many, but not all, environmental conditions.
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PMID:The protein phosphatases of Synechocystis sp. strain PCC 6803: open reading frames sll1033 and sll1387 encode enzymes that exhibit both protein-serine and protein-tyrosine phosphatase activity in vitro. 1610 28

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 can fix N(2) when combined nitrogen is not available in the growth medium. It has a family of 13 genes encoding proteins with both a Ser/Thr kinase domain and a His kinase domain. The function of these enzymes is unknown. Two of them are encoded by pkn41 (alr0709) and pkn42 (alr0710). These two genes are separated by only 72 bp on the chromosome, and our results indicate that they are cotranscribed. The expression of pkn41 and pkn42 is induced by iron deprivation irrespective of the nature of the nitrogen source. Mutants inactivating either pkn41, pkn42, or both grow similarly to the wild type under normal conditions, but their growth is impaired either in the presence of an iron chelator or under conditions of nitrogen fixation and iron limitation, two situations where the demand for iron is particularly strong. Consistent with these results, these mutants display lower iron content than the wild type and a higher level of expression for nifJ1 and nifJ2, which encode pyruvate:ferredoxin oxidoreductases. Both nifJ1 and nifJ2 are known to be induced by iron limitation. NtcA, a global regulatory factor for different metabolic pathways, binds to the putative promoter region of pkn41, and the induction of pkn41 in response to iron limitation no longer occurs in an ntcA mutant. Our results suggest that ntcA not only regulates the expression of genes involved in nitrogen and carbon metabolism but also coordinates iron acquisition and nitrogen metabolism by activating the expression of pkn41 and pkn42.
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PMID:A pair of iron-responsive genes encoding protein kinases with a Ser/Thr kinase domain and a His kinase domain are regulated by NtcA in the Cyanobacterium Anabaena sp. strain PCC 7120. 1678 91

The genome of the cyanobacterium Anabaena PCC 7120 encodes seven polypeptides showing sequence similarities with peroxiredoxins (Prx-s). One of them, prxQ-A (alr2503), which encodes a Prx Q homologue, is located in the same gene cluster as pkn22, which encodes a Ser/Thr kinase. Here we report that the pkn22-knockout mutant (Mp22) is sensitive to oxidative stress because it fails to synthesize PrxQ-A; the expression of prxQ-A is significantly induced under oxidative stress conditions. The hypersensitivity of the Mp22 mutant to oxidative stress was restored by inducing the expression of the prxQ-A gene in trans. The recombinant PrxQ-A protein shows antioxidant activity protecting the DNA from being degraded by reactive oxygen species, catalyzes the reduction of H2O2 in the presence of DTT, and shows thioredoxin-dependent peroxidase activity in vitro. The conserved Cys47 residue is the peroxide oxidation site, since the replacement of Cys47 by a Ser residue completely abolished the peroxidase activity. All these data suggest that PrxQ-A may efficiently protect this organism from oxidative stress.
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PMID:PrxQ-A, a member of the peroxiredoxin Q family, plays a major role in defense against oxidative stress in the cyanobacterium Anabaena sp. strain PCC7120. 1721 Apr 55

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 can fix N(2) under oxic conditions, and the activity of nitrogen fixation occurs exclusively in heterocysts, cells differentiated from vegetative cells in response to a limitation of a combined-nitrogen source in the growth medium. At the late stages of heterocyst differentiation, an envelope layer composed of two glycolipids is formed to limit the entry of oxygen so that the oxygen-sensitive nitrogenase can function. The genome of Anabaena sp. strain PCC 7120 possesses a family of 13 genes (the hstK family), all encoding proteins with a putative Ser/Thr kinase domain at their N termini and a His-kinase domain at their C termini. In this study, we showed that the double mutant D4.3 strain, in which two members of this gene family, pkn44 (all1625) and pkn30 (all3691), were both inactivated, failed to fix N(2) in the presence of oxygen (Fox(-)). In an environment without oxygen, a low level of nitrogenase activity was detectable (Fix(+)). Heterocyst development in the mutant D4.3 was delayed by 24 h and arrested at a relatively early stage without the formation of the glycolipid layer (Hgl(-)). Only the minor species of the two heterocyst-specific glycolipids (HGLs) was missing in the mutant. We propose that DevH, a putative transcription factor, coordinates the synthesis of both HGLs, while Pkn44/Pkn30 and the previously characterized PrpJ may represent two distinct regulatory pathways involved in the synthesis of the minor HGL and the major HGL, respectively.
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PMID:Two genes encoding protein kinases of the HstK family are involved in synthesis of the minor heterocyst-specific glycolipid in the cyanobacterium Anabaena sp. strain PCC 7120. 1751 80

The Pho regulon is controlled by the histidine kinase-response regulator pair SphS-SphR in many cyanobacteria and up-regulation of the Pho regulon can be monitored by measuring alkaline phosphatase activity. However, the mechanism regulating signal transduction between SphS and SphR has not been described. We have created a cyanobacterial strain allowing the introduction of mutations into the transmitter domain of SphS. Mutations at Thr-167, adjacent to the H motif of SphS, introduce elevated alkaline phosphatase activity in the presence of phosphate and an enhancement of alkaline phosphatase activity, when compared to the control strain, in phosphate-limiting media. SphU acts as a negative regulator of the SphS-SphR system in Synechocystis sp. PCC 6803 and we show that constitutive alkaline phosphatase activity in the absence of SphU requires signal transduction through SphS and SphR. However, constitutive activity in the absence of SphU is severely attenuated in the DeltaSphU:SphS-T167N mutant. Our data suggest that Thr-167 contributes to the mechanism underlying regulation by SphU. We have also assembled a deletion mutant system allowing the introduction of mutations into SphR and show that Gly-225 and Trp-236, which are both conserved in SphR from cyanobacteria, are essential for activation of the Pho regulon under phosphate-limiting conditions.
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PMID:Phosphate sensing in Synechocystis sp. PCC 6803: SphU and the SphS-SphR two-component regulatory system. 1754 76

Absorbance difference spectra associated with the light-induced formation of functional states in photosystem II core complexes from Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 (e.g., P(+)Pheo(-),P(+)Q(A)(-),(3)P) are described quantitatively in the framework of exciton theory. In addition, effects are analyzed of site-directed mutations of D1-His(198), the axial ligand of the special-pair chlorophyll P(D1), and D1-Thr(179), an amino-acid residue nearest to the accessory chlorophyll Chl(D1), on the spectral properties of the reaction center pigments. Using pigment transition energies (site energies) determined previously from independent experiments on D1-D2-cytb559 complexes, good agreement between calculated and experimental spectra is obtained. The only difference in site energies of the reaction center pigments in D1-D2-cytb559 and photosystem II core complexes concerns Chl(D1). Compared to isolated reaction centers, the site energy of Chl(D1) is red-shifted by 4 nm and less inhomogeneously distributed in core complexes. The site energies cause primary electron transfer at cryogenic temperatures to be initiated by an excited state that is strongly localized on Chl(D1) rather than from a delocalized state as assumed in the previously described multimer model. This result is consistent with earlier experimental data on special-pair mutants and with our previous calculations on D1-D2-cytb559 complexes. The calculations show that at 5 K the lowest excited state of the reaction center is lower by approximately 10 nm than the low-energy exciton state of the two special-pair chlorophylls P(D1) and P(D2) which form an excitonic dimer. The experimental temperature dependence of the wild-type difference spectra can only be understood in this model if temperature-dependent site energies are assumed for Chl(D1) and P(D1), reducing the above energy gap from 10 to 6 nm upon increasing the temperature from 5 to 300 K. At physiological temperature, there are considerable contributions from all pigments to the equilibrated excited state P*. The contribution of Chl(D1) is twice that of P(D1) at ambient temperature, making it likely that the primary charge separation will be initiated by Chl(D1) under these conditions. The calculations of absorbance difference spectra provide independent evidence that after primary electron transfer the hole stabilizes at P(D1), and that the physiologically dangerous charge recombination triplets, which may form under light stress, equilibrate between Chl(D1) and P(D1).
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PMID:Spectroscopic properties of reaction center pigments in photosystem II core complexes: revision of the multimer model. 1833 36

The inactivation of sll0776 (spkD), a gene encoding a protein Ser/Thr kinase in Synechocystis PCC 6803, led to a pleiotropic phenotype of the SpkD null mutant. This mutant is impaired in its growth ability under low concentration of inorganic carbon (C(i)), though its C(i)-uptake system is not affected. Addition of glucose, phosphoglyceraldehyde or pyruvate does not allow the mutant to grow under low-C(i) conditions. In contrast, this growth defect can be restored when the low-C(i) culture medium is supplemented with metabolites of the TCA cycle. Growth of the mutant is also inhibited when ammonium is provided as nitrogen source, whatever the carbon regime of the cells, due to the high demand for 2-oxoglutarate, which is the carbon skeleton for ammonium assimilation. When mutant cells are cultured under standard growth conditions, the intracellular concentration of 2-oxoglutarate is 20 % lower than is observed in the wild-type strain. However, this decrease of 2-oxoglutarate level only slightly affects the phosphorylation state of PII, a protein that regulates nitrogen and carbon metabolism according to the intracellular levels of 2-oxoglutarate. Properties of the SpkD mutant suggest that the Ser/Thr kinase SpkD could be involved in adjusting the pool of the TCA cycle metabolites according to C(i) supply in the culture medium.
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PMID:Inactivation of spkD, encoding a Ser/Thr kinase, affects the pool of the TCA cycle metabolites in Synechocystis sp. strain PCC 6803. 1859 43

The aim of the current study was to determine whether the FcgammaRIIb 187-Ile/Thr polymorphism is a predisposition factor for subtypes of RA defined by disease severity and production of autoantibodies against cyclic citrullinated peptides (anti-CCPs) in Taiwanese RA patients. Genotype distributions and allele frequencies of FcgammaRIIb 187-Ile/Thr were compared between 562 normal healthy controls and 640 RA patients as stratified by clinical parameters and autoantibodies. Significant enrichment of 187-Ile allele was observed in RA patients positive for anti-CCP antibodies as compared with the anti-CCP negative RA patients (P=0.001, OR 1.652 (95% CI 1.210-2.257)) or as compared with the normal controls (P=0.005, OR 1.348 (95% CI 1.092-1.664)). In addition, 187-Ile allele was found to be enriched in RA patients positive for rheumatoid factor (RF) compared to the RF negative RA patients (P=0.024, OR 1.562 (95% CI 1.059-2.303)). Furthermore, the homozygotes were enriched in destructive male RA patients (P=0.035; OR 2.038 (95% CI 1.046-3.973)) and the 187-Ile allele was associated with early-onset of RA in Taiwanese patients (P=0.045, OR 1.548 (95% CI 1.007-2.379)). Thus, FcgammaRIIb SNP 187-Ile/Thr may influence the RA phenotypes in Taiwanese RA.
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PMID:A transmembrane polymorphism in FcgammaRIIb (FCGR2B) is associated with the production of anti-cyclic citrullinated peptide autoantibodies in Taiwanese RA. 1863 24


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